Cell phone exchange

Please note review is on behalf of my mother inlaw. My family and i have had the worse experience with american swiss. We purchased a cell phone via Account and the very same day as my son used the phone added his whatsapp etc the phone started to heat up immediately the very next next day we took the phone back to shop where the sales assistant booked the phone and sent it away for check ups with the technician. They claim there is absolutely nothing wrong with the phone me being polite 2 weeks later of impatiently going back and forth to the store to find out feedback as communication from the sales assistant and store manager wasn't very accommodating. We simply asked for a exchange on the phone not even credit back just a exchange, i was told that they could not grant my exchange which i could not understand as the phone was immediately returned and as a customer i have the right to fairness and within a 7 day period the phone could be exchanged or refunded. What frustrates me the most is that the sales assistant assured us that we could do a exchange and 2 weeks later she changed her story which me , my son and daughter inlaw all witnessed. Sadly they failed to assist me on simply getting a exchange which should be such a easy process if all the necessary requirements is in place. As a customer and someone who worked in the retail industry i know that our rights has been violated. I am currently still waiting on feedback from the store the manager was no help at all and we still waiting to do a simple exchange how ridiculous whatever problems they have with their suppliers should not be the customers problem and they should be able to fix the matter, I dont advise anyone to make the same mistake please be careful when purchasing cellphones from them.